The present invention relates to the fields of microbiology and immunology and more specifically relates to compositions and methods for diagnosing taeniasis. In particular, the invention pertains to isolated adult Taenia solium antigens and their use in immunoassays.
Taenia solium, also referred to as the pork tapeworm, is a helminth that exists in both a mature tapeworm form and a larval form. The lifecycle of T. solium begins when a pig, the intermediate host, ingests tapeworm eggs excreted in the feces of a tapeworm carrier. The larvae hatch from the eggs and invade most tissues of the pig, giving rise to the disease cysticercosis.
When humans ingest raw or undercooked meat from cysticercotic pigs, tapeworm, or taeniasis, develops. Patients with taeniasis exhibit symptoms such as epigastric discomfort, nausea, insomnia, anorexia, irritability, diarrhea and weight loss. Occasionally, individual segments of the tapeworm that are self-contained hermaphroditic reproductive units, referred to as proglottids, may obstruct the appendix, biliary duct, or pancreatic duct, causing severe pain and possible organ damage. These infected individuals become carriers of the tapeworm which produces eggs that are excreted in the feces, thereby continuing the life cycle of the parasite.
Humans may ingest T. solium eggs present in contaminated food and water and serve as intermediate hosts. After T. solium eggs are ingested, cysticerci may develop in the subcutaneous tissues, muscles, heart, lungs, liver, brain, and eye. Although small numbers of viable cysticerci fail to produce symptoms in the infected host, death of the larvae stimulate a marked inflammatory reaction, fever, muscle pains, and eosinophilia. If the larvae invade the central nervous system, the host may present with meningoencephalitis, epilepsy, and other neurologic or psychiatric manifestations.
The various manifestations of neurologic dysfunction caused by T. solium infection are collectively termed neurocysticercosis. Although neurocysticercosis can include many neurological symptoms, epilepsy is the most common symptom. In fact, T. solium is considered the leading infectious cause of epileptic seizures worldwide. Additionally, T. solium/neurocysticercosis has a current worldwide toll of 50 million cases with 50,000 deaths each year.
Neurocysticercosis is rarely acquired in the United States; however, the disease is common in Latin America, Asia, Russia and Eastern Europe. In Mexico, the mean rate for cysticercotic pigs in inspected slaughterhouses during 1980-1981 was 1.55%, and in rural areas of Mexico and South America where sewage disposal is limited, the number of cysticercotic pigs can be in excess of 5%. In these and other developing countries, the parasite causes a substantial economic burden to the pork industry. Additionally, due to the increased travel and immigration from highly endemic areas, detection and treatment of T. solium-related diseases has become a U.S. public health priority.
Because humans are the primary hosts of the tapeworm parasite, the diagnosis and treatment of adult tapeworm carriers is crucial for interrupting transmission of taeniasis and cysticercosis. Furthermore, distinction between the adult and larval forms of T. solium is important since both infections are asymnptomatic initially, but result in two different diseases, taeniasis and cysticercosis, respectively, which require two different routes of treatment.
Classically, taeniasis has been detected by direct parasitologic examination of stool samples. Detection methods, based on microscopic observation of eggs or proglottids in feces, are neither sensitive nor specific. Direct examination of Taenia eggs is equivocal and requires examination of expelled proglottids for speciation. Recently, coproantigen detection assays have been developed. However, these assays are not specific for T. solium. For example, they are unable to distinguish between T. solium and T. saginata infections. A more recent method involving DNA probes specific for T. solium or T. saginata has been developed that uses species-specific primers to differentiate these two tapeworm infections. This technique relies on the amplification of parasite DNA obtained from parasite eggs or proglottids present in the stool sample. Although the polymerase chain reaction can detect the presence of a single egg, the intermittent passage of eggs in the stool limits the usefulness of this assay.
An early and specific diagnosis of taeniasis may prevent cysticercosis and allow treatment for taeniasis before painful symptoms arise. Therefore, there is a need for sensitive, specific, and inexpensive assays that can detect the presence of the T. solium adult worm.
Compositions and methods for detecting and diagnosing Taenia solium are provided herein. The compositions contain one or more of the T. solium polypeptides described below. The polypeptides are useful in immunoassays for the detection of T. solium in biological samples. The preferred polypeptides are specific to the adult form of T. solium. The polypeptides are useful as diagnostic agents for the detection of adult tapeworm infection. More preferably, the polypeptides are T. solium glycoprotein antigens referred to herein as T. solium excretory/secretory (TS/ES) polypeptides. The most preferred TS/ES polypeptide is one having a molecular weight of approximately 33 kDa, 38 kDa, or 42 kDa as determined by SDS-PAGE analysis. The compositions also include combinations of these preferred polypeptides or T. solium peptides, which are fragments of the TS/ES polypeptide. Preferred polypeptides and fragments thereof are immunoreactive with T. solium antibodies. The preferred polypeptides and fragments thereof are specific for T. solium and are not cross-reactive with antibodies present in T. saginata serum samples.
The preferred methods provided in herein are immunoassays directed toward the detection of T. solium antibodies in biological samples such as biological fluids. The assays detect antibodies to the adult T. solium organism and are thereby capable of distinguishing between infection by the adult tapeworm and larval forms of T. solium. The preferred immunoassay utilizes one or more of the isolated TS/ES adult antigens or immunoreactive portions thereof, as described herein, for the detection of anti-TS/ES antibodies in the biological sample. The polypeptides, or antigens, are preferably labeled, either directly or indirectly with a detectable label, such as a radioisotope or a detectable molecule or protein.
Diagnostic and analytical methods and kits may be developed for detection and measurement of T. solium antibodies in a variety of biological samples. The method and kit can be in any configuration well known to those of ordinary skill in the art.
Accordingly, it is an object of the present invention to provide means for detecting T. solium carriers and thus prevent the spread of T. solium from one host to another.
It is another object of the present invention to provide a method for the detection of T. solium, particularly T. solium infection in humans, that is sensitive and accurate.
It is another object of the present invention to provide a sensitive method for the diagnosis of taeniasis.
It is another object of the present invention to provide a diagnostic method capable of distinguishing adult T. solium infection from larval T. solium infection (cysticercosis).
It is another object of the present invention to provide a diagnostic method capable of distinguishing adult T. solium infection from other helminthic infections, particularly T. saginata infections.
It is yet another object of the present invention to provide a rapid, simple, and inexpensive immunoassay for the detection of antibodies to adult T. solium in an easily obtained biological fluid such as blood serum, plasma or saliva.
One advantage of the invention described herein is that the methods are rapid and simple to conduct, and the results can be interpreted without the use of instrumentation or special temperature conditions, which is optimal for use in poor, underdeveloped countries where T. solium is often endemic.
These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.